(a) Field of the Invention
The present invention relates generally to omni directional antennas. More particularly, it relates to an omni directional antenna having a shaped reflector.
(b) Description of Related Art
Bicone antennas are commonly used to produce omni directional radio frequency radiation patterns. An omni directional radiation pattern provides a wide angle of coverage, which is especially advantageous in mobile communications applications. A single bicone antenna generally comprises a waveguide, two feedprobes, three polarizing pins, a plurality of radiating slots, and two reflectors. Typically, an electrical radio frequency input is applied to one of the feedprobes, and the other feedprobe is loaded with a termination or connected to another channel for redundant operation. The feedprobes are coplanar and are spaced 90.degree. apart along the wall of the waveguide.
The energized feedprobe produces linearly polarized waves, within the waveguide, that are converted into circularly polarized waves by the polarizing pins. These circularly polarized waves form a standing wave between the reflectors that excites a series of longitudinal or transverse slots in the waveguide to radiate linearly polarized waves.
This conventional omni directional antenna design has several drawbacks. For example, an expensive, bulky polarizer shield is needed to prevent multipathing effects due to leakage through the walls of the waveguide. In addition, assembly and material costs are high because two reflectors must be precisely mounted to the waveguide.
These disadvantages become even more apparent for applications that require a dual-band antenna. Historically, a dual bicone antenna is used for dual-band applications. Essentially, a dual bicone antenna consists of two single bicone antennas joined to a common waveguide.